DESIGN & MANUFAC LAB
DESIGN & MANUFAC LAB EML 2322
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This 5 page Class Notes was uploaded by Paige Cruickshank on Friday September 18, 2015. The Class Notes belongs to EML 2322 at University of Florida taught by Staff in Fall. Since its upload, it has received 11 views. For similar materials see /class/206709/eml-2322-university-of-florida in Engineering Mechanical at University of Florida.
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Date Created: 09/18/15
EML 2322L MAE Design and Manufacturing Laboratory Drilling Speeds and Feeds The speed of a drill is usually measured in terms of the rate at which the outside or periphery of the tool moves in relation to the work being drilled The common term for this is quotSurface Feet per Minutequot abbreviated as sfm Every tool manufacturer has a recommended table of sfm values for their tools General sfm guidelines are also commonly found in resources such as the Machiner Handbook see Table l in this document The peripheral and rotational velocities of the tool are related as shown in the following equation V7rDN 111 where Vis the recommended peripheral velocity for the tool being used D is the diameter of the tool N is the rotational velocity of the tool Since the peripheral velocity is commonly expressed in units of feeUmin and tool diameter is typically expressed in units of inches Equation 1 can be solved for the spindle or tool velocity N in the following manner Nrpm 12 Vsfm7r Din Eq 2 Equation 2 will provide a guideline as to the maximum rpm when drilling standard materials The optimum speed for a particular setup is affected by many factors including the following Composition amp hardness of material Depth of hole Efficiency of cutting uid Type condition and stiffness of drilling machine Stiffness of workpiece fixture and tooling shorter is better Quality of holes desired Life of tool before regrind or replacement Table 2 contains recommended feeds for various drill diameters For each diameter range there is a corresponding feed range Use the smaller values for stifferharder materials and the larger values for softer materials To calculate the feedrate use the following formula fNfr Eq 3 where f feedrate N spindle speed rpm f feed per revolution inrev In addition the following rules of thumb should be observed when applicable On most jobs it is usually better to start with a slower speed and build up to the maximum after trials indicate the job can run faster Overloading the drill bit by feeding too quickly in Z will result in an excessive chipload on each drill lip causing the cutting edges to fracture chip Feeds and speeds should be reduced up to 50 when drilling holes deeper than 3 drill diameters The deeper the hole the greater the tendency is for chips to pack and clog the utes of the drill This increases the amount of heat generated and prevents the coolant from conducting heat away from the point Excessive buildup of heat at the point will eventually result in premature failure Peck drilling or the practice of drilling a short distance then withdrawing the drill will reduce the chip packing The deeper the hole the more frequent the drill must be retracted or pecked to be effective 0 A reduction in speed and feed to reduce the amount of heat is generally required in most deephole applications where coolant cannot be effectively applied TABLE 1 Recommended HSS Speeds for Common Materials Material Aluminum and its alloys Bronze high tensile Cast Iron soft Cast Iron medium hard Cast Iron hard chilled Hastelloy Inconel Magnesium and its alloys Monel High nickel steel Mild steel 23 C Steel 45 C Tool steel Forgings Steel alloys 300400 Brinell Heat Treated Steels 3540 Rockwell C 4045 Rockwell C 4550 Rockwell C 5055 Rockwell C stainless steel free machining stainless work hardened Titanium alloys Recommended Speed V surface ftmin TABLE 2 Recommended Feeds for 2 Flute HSS Drills Drill Diameter Recommended Feed f in inlrev under 18 0001 to 0003 18 to 1 0002 to 0006 14 to 12 0004 to 0010 12 to 1 0007 to 0015 1 and over 0015 to 0020 Final Notes 0 Remember that the speed and feed calculated using the manufacturer s empirical data ie Tables 1 amp 2 are the optimum parameters In other words these are the maximum speed and feedrate that could be used under perfect conditions To promote their products this published data is usually on the optimistic side ie the speeds and feeds are typically on the high side 0 Running a tool too slow will only decrease productivity On the other hand running a tool too fast with regard to speed or feedrate will either result in accelerated tool wear or outright failure So always err on the side of running too slow Example Calculate the speed and feed for a 1A HSS drill bit in soft cast iron First lookup the recommended surface speed peripheral velocity in Table V2 100 fUmin Next calculate the spindle speed from Equation 2 Nrpm 12 V7rD 12 inft 100 fUminn 025 in 1500 rpm ans Now calculate the feedrate used for plunging in the Z aXis From Table 2 lookup the recommended feed per revolution for a 14 HSS drill bit f 2 0003 inrev Finally calculate the plunge feedrate using Equation 3 finmin Nrpm fr inrev 1500 revmin 0003 inrev 45 inmin ans Note that these speed and feed values are guidelines assuming proper ooded lubrication workpiece stiffness and drill depth less than 3 drill diameters 075 When applying the lubricant manually as in the lab scale the feed and speed back to 60 so N 900 rpm and f 27 inmin
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